1. U.S. Pat. No. 4,602,174
2. Disclosure Document no. 172295
The invention is in the general field of reciprocating permanent magnet AC electric motors and generators. Specifically, it is a means of generating magnetic centering forces to confine reciprocating magnets within the air gaps of such machines.
Reference 1 discloses an AC electrical machine that can be used either as a generator to convert reciprocating motion of a permanent magnet ring to AC voltage, or as a motor to convert AC voltage to reciprocating motion of a permanent magnet ring. Referring to FIG. 4 of Reference 1, permanent magnets 50 reciprocate in a left-right direction, and if the machine is conventionally designed, there will be no force on the permanent magnets if there is no current in armature coil 56, provided the magnets do not emerge from the air gaps. If the magnets do so emerge, strong magnetic forces are generated that expel the magnets further. To prevent emergence of the magnets and their subsequent expulsion from the air gap, mechanical and/or magnetic centering springs have been used in prior art. The latter are disclosed in Reference 2. Centering springs introduce complication and increase cost. The object of the present invention is to provide magnetically generated centering force on the reciprocating magnets without adding cost or complexity.
In the invention, the ferromagnetic structure (60,62,64,68 of FIG. 6, Reference 1) is designed unconventionally in that all or part of it is allowed to magnetically saturate as permanent magnets 50 of Ref. 1 approach the left or right extremes of the air gap in which they reciprocate. Theory shows, and experiment confirms, that magnetic saturation causes a force to be exerted on the reciprocating magnets in a direction such as to confine the magnets within the air gap. Conventional design avoids magnetic saturation because it degrades performance by lowering efficiency, and, in the case of generators, distorts output voltage waveform. In a linear motion AC motor-generator of the type disclosed in Ref. 1 but modified according to the invention, it is found that useful centering forces can be generated without incurring a significant performance penalty.